The present invention relates to a piston for a two-cycle internal combustion engine.
Among two-cycle internal combustion engines for portable-type power-driven working machines, there is one constructed in such a manner that a lower end of a skirt portion of a piston reciprocating within a cylinder passes an opening portion of an inlet port defined on the cylinder to open and close the inlet port, thereby allowing an air-fuel mixture to flow from the inlet port through a lower space of the cylinder into a crankcase, as well as shutting off the same. Conventionally, a piston used in such internal combustion engine is ordinarily provided with a plane end edge at a lower end of its skirt portion. Because the plane lower end edge opens and closes the inlet port of the cylinder, when the piston reciprocates upwardly and downwardly within the cylinder, the lower end edge of the skirt portion of the piston opens and closes the inlet port rapidly. For this reason, an abrupt pressure change is caused at that portion and large pressure wave is generated, which results in a problem that a considerably high-level intake noise is caused from the engine. In order to solve this problem, there is known a piston or a cylinder which is adapted to gradually open and close the inlet port at the primary stage during opening and closing the opening of the inlet, by forming a notch at a lower end of a skirt portion of the piston or an inlet port of the cylinder, whereby the occurrence of a high-level intake noise is restrained. However, such a structure that the notch is provided on the piston or the cylinder is difficult to be manufactured and a strength of the portion where the notch is provided is weakened, so that there is some problems, for example, an unexpected early breakage of the piston or the cylinder is apt to occur.